Field of the Invention
This invention relates to a three-dimensional shape measurement apparatus that measures a three-dimensional shape of a specimen in a non-contacting manner.
Description of the Related Art
In order to make industrial products smaller and more advanced, the functionality of a surface of a component is important. For example, a surface of a cylinder of an automotive engine is provided with intentional microasperity for controlling sliding resistance, which results in improving energy efficiency and increasing longevity. In the field of dental implants, features adaptive to a living body are managed not only on the basis of materials but also on the basis of roughness of surface (surface texture).
Further, in addition to these functional and biological features, various functions including an electrical function such as contact resistance of an electrical contact, an optical function such as a reflection and scattering, and a surface function related to a design factor such as appearance have been required for a component.
Needless to say, in order to control the quality of the surface function, it is important to correctly measure a geometric shape of a surface of a component for quantification.
As one of the methods for measuring a geometric shape of a surface of a component, a stylus surface roughness meter disclosed in Industrial Standard ISO3274:1996 set by the International Organization for Standardization (ISO) (for the Japanese version, see B0651:2001, Japanese Industrial Standards (JIS)) has long been used. This method permits obtaining of highly reliable data because a solid surface of an object to be measured is accurately traced with a mechanical stylus tip.
On the other hand, non-contacting measurement apparatuses that employ various measurement principles have also been widely used. The non-contacting measurement apparatuses have been rapidly spread in recent years because they can easily perform measurement without scratching an object to be measured. Typical non-contacting measurement apparatuses are classified in the Industrial Standard ISO25178-6:2010 (for the Japanese version, see B0681-6:2014, JIS) by putting the standard in place, so it is understood that they have started being widely used in industry.
Many of the non-contacting measurement apparatuses employ an optical approach. For example, as disclosed in Japanese Patent No. 3960862 and Japanese Patent No. 3847422, a measurement apparatus that employs confocal microscopy or coherence scanning interferometry is a typical example of the non-contacting measurement apparatuses available in the market.
In addition to the measurement apparatuses described above, there exist various non-contacting optical measurement apparatuses. Further, even for measurement apparatuses employing the same measurement principle, there exist a plurality of measurement conditions depending on, for example, the magnification of an objective. The measurement performance and the limit of measurement depend on the used measurement apparatus or the used measurement conditions. In this way, it is greatly industrially advantageous if an appropriate measurement apparatus can be selected from among various types of measurement apparatuses according to the measurement purpose, that is, the measurement accuracy, the size of an area to be measured, or the cycle time.
On the other hand, when a measurement apparatus or a measurement condition is not optimally selected, an incorrect measurement result may be output by erroneously detecting, for example, noise if measurement is performed in an area in which the limit of measurement is exceeded. In order to obtain a correct measurement result, it is necessary to recognize that there exists incorrect measurement data, which requires plenty of experience and skill in using a measurement apparatus. There is a possibility that a correct measurement result will not be obtained and then a correct analysis will not be performed because the existence of incorrect measurement data is not recognized.